Previously, reactions of lignin materials involving sodium nitrite have related to its use at low temperatures in promoting diazo coupling reactions and for introducing nitro groups. Such reactions have been conducted under acidic conditions (in acid, sodium nitrite is converted to nitrous acid). While nitrous acid has been used for nitration of lignin, the prinicpal reagent used is nitric acid.
It has recently been found that one can avoid the degrading effects of nitrating lignosulfonates with nitric acid by employing mixtures of sodium nitrate and nitrite salts. These reactions are carried out in the 60.degree.-90.degree. C. range with a pH around 8.7-9.0. Under these reaction conditions, nitro radicals are formed and react with the lignosulfonates leading to organically bound nitrogen contents of 1.2-1.4% in the reaction product.